Ultraviolet lamp



Jan. 8, 1957. I F.' H. RIXTON 2,777,091

ULTRAVIOLET LAMP Filed April so, 1952- 0 I000 I 2000 JOOO 4W0 Hal/e6 z/FE INVENTOR EH-Pam.

' 'ATTO'RNEY United States Patent ULTRAVIOLET LAMP Frederick H. Rixton, Livingston, N. 1., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 30, 1952, Serial No. 285,151

4 Claims. (Cl. 31548) The present invention relates to discharge lamps and, more particularly, to discharge lamps for the generation of ozone producing radiations.

The principal object of my invention is to provide a lamp which has a high output of ozone-producing 1850 A. U. radiations which are useful in destroying odors.

Another object of my invention is to produce a discharge lamp which has a high output of 1850 A. U. radiation, a long life and starts readily when the proper voltage is applied.

A further object of my invention is to produce a lamp for destroying odors and which also has a germicidal efiect due to the generation of 2537 A. U. radiation.

A still further object of-my invention is to produce a discharge lamp which has an envelope which will transmit a large percentage of 1850 A. U. radiation as well as 2537 A. U. radiation.

The above objects, and other objects which will become apparent as the description proceeds, are accomplished by utilizing a glass for the envelope of the discharge lamp which will transmit a large percentage of 1850 A. U. radiation and by controlling the proportion of current flowing in the discharge within the lamp and through the filament by-passing the discharge.

The following description will be better understood by reference to the accompanying drawing in which:

Figure 1 is an elevational view of a discharge lamp constructed according to my invention.

Figure 2 is a graph showing the output of my improved lamp as compared to that of the lamps of the prior art.

I have found that the output of prior art lamps with .respect to 1850 A. U. radiations may be increased by more than a factor of two, while improving slightly the output of 2537 A. U. radiation, by properly selecting the glass for the envelope and by controlling the proportion of current flowing between the electrodes of the discharge lamp. In Figure 1, the lamp is designated generally by the reference numeral and is comprised of an envelope 12 based with a standard threaded base 15 at one end thereof. Sealed into the base end of the envelope 12 is stem 16 closed by a press 18. Passing through the press 18 and supported thereby are lead-in conductors 20. The conductors 20 extend exteriorly of the lamp envelope 12 and make electrical connection with the base 16 to provide a means of supplying power to the discharge lamp 10. The lead-in conductors 20 also extend interiorly of the envelope 12 and the interior ends thereof are bent toward each other and then downwardly thereby forming a hook at each end of the conductors. The hooked ends of the conductors 20 form the electrode surfaces 21 which act as anodes. Between the lead-in conductors 20 and supported by and extending from the press 18 is an anchor 22 whose end is olfset from the interior ends of the lead-in conductors 20. The anchor 22 which is shorter than the part of the lead-in conductors 20 which extend interiorly of the envelope provides a fastening point for the center of a two section filament 24. Each section of the filament 24 consists of a coiled wire preferably of tungsten. The

2,777,lll Patented Jan. 8, 1957 filament extends from the bottom of the hook of one of the conductors 20 to the anchor 22 and from the anchor 22 to the bottom of the hook of the other conductor 20 thereby providing a vertical -shaped filament connected in parallel with the electrodes 21. The outside end of each coiled filament section 25 is coated with an emission material 26 which may consist of the usual alkaline earth oxide. The envelope 12 is filled with a gaseous medium such as argon preferably at a pressure between approximately 3.5 and 4.5 mm. of mercury and has mercury vapor admixed therewith. If the pressure of the gaseous medium exceeds 4.5 mm. the lamp will be difi icult to start and if the pressure is lower than 3.5 mm. sputtering of the emission material is likely to occur.

In operation, an A. C. voltage is applied to the lamp and the voltage drop across the filament 24 causes a glow discharge between the coated ends of the filament 24 and the electrodes 21 due to the ionization of the gas within 1 the envelope and the heating of the emission material on the filament. Of the total current drawn by the lamp, part flows through the filament 24 and the remainder flows in the glow discharge between the electrodes 21 and the ends of the filament 24. While we have provided anodes 21 the discharge will occur in the absence of electrodes 21 since the leads and the end of the filaments will act as anodes. The lamp We have described operates as the lamp shown in Patent 2,392,333 to Chalmers More head issued January 8, 1946. While the drawing shows a two section filament, two separate filaments may be used and it is not necessary, as is obvious to one skilled in the art, to restrict the structure to a true V form.

I have found that if the resistance of the filament is such that approximately 40 to 51% of the current is carried by the filament and about 60 to 49% of the current is carried by the discharge between the remote ends of the filament, the lamp will have a long life as well as a high output of 1850 A. U. radiation as compared with the lamps of the prior art. This increase in the output of 1850 A. U. radiation is accomplished with an accompanying slight improvement in 2537 A. U. radiation output which is desirable for its germicidal effect.

I have also found that lamps, wherein the current is as specified above, start easier than the lamps of the prior art. This easier starting is important in areas where the voltage supply is subject to fluctuations. The lamp is designed to operate on A. C. supplies of between and volts. When the discharge within the lamp occurs, the voltage drop across the filament and the discharge should be limited to approximately 10 volts. Therefore, a standard ballast, either inductive, capacitive, or resistive, is connected in series with the lamp to limit the lamp voltage drop after starting to 10 volts.

The resistance of the filament 24 should be between approximately 14 and 17.5 ohms to assure that the correct proportion of current will flow in the discharge between the lamp electrodes. I prefer to use a resistance of 15.5 ohms which will cause 55% of the current to be carried by the discharge. By limiting the resistance of the filament to the specified range, a high output of 1850 A. U. will be assured. Operating at voltages between 110 v. and 125 v. with a ballast that limits lamp voltage to about 10 volts after starting the lamp will draw approximately 0.3 to 0.4 ampere and approximately 49 to 60% of the current of the lamp will be carried by the discharge between the electrodes 21 and the ends of the filament 24. The specified resistance of the filament will also assure easy starting in the above voltage range. Once the lamp has started, the operating voltage of the lamp is about 10 volts, and therefore, the power input to the lamp is approximately 3 /2 watts. In the lamps of the prior art the resistance of the filament was 13 ohms and the operating voltage for these prior art lamps was 10 volts.

V In order to utilize the higher output of 1850 A. U. I have found that it is necessary to use a borosilicate glass which has aluminum oxide and sodium oxide therein. The composition of the above glass is approximately as follows:

Components: Parts by weight SiOz 65 A1203 NazO 2 LiOz and CaO Balance The above glass also has impurity traces of FezOs and T102 therein. In producing a glass having a high transmissibility of 1850 A. U., the FezOa impurity must be kept at a minimum. In so doing a glass can be produced which will transmit at least 27 percent of 1850 A. U. radiation and at least 75 percent of 2537 A. U. radiation. The glasses normally used heretofore for envelopes will at the best transmit about of 1850 A. U. along with about 70 percent 2537 A. U.

The lamp of the present invention will have a high 1850 A. U. output with respect to the prior art as shown in the graph of Figure 2. Curve A represents the output of my improved lamp While curve B shows the output of the prior art lamps having a filament resistance of 13 ohms. It will be seen that the lamp has more than double the 1850 A. U. output of the prior lamps. The output of 1850 A. U. was measured by a platinum photo tube connected in a bridge circuit employing a galvanometer for directly reading relative 1850 A. U. radiation. The values on the graph indicating the amount of 1850 A. U. output are arbitrary units as measured by galvanometer deflection.

It will be seen from the above that the present invention provides an improved lamp for generating 1850 A. U. radiation while also improving slightly the output of 2537 A. U. radiation. The lamp will have a long life and will start readily.

I claim:

1. An electric discharge lamp having a high output of 1850" A. U. radiation comprising an envelope having a gaseous filling at a pressure between approximately 3.5 and 4.5 mm. and admixed with mercury vapor, a pair of lead in conductors extending interiorly of said envelope, an anchor between said lead in conductors and olfset from the ends thereof, a coiledfilament section between the interior end of each of said lead in conductors and said anchor, each of said filament sections being coated with emission material about the end of said section adjacent the interior end of said conductors, the resistance of said filament sections being such that about 40 to 51% of the current of said lamp is carried by said filament when a sufficient voltage is applied to said lamp to cause a glow discharge between the coated ends of said filament, and said envelope being formed of a glass having a high transmissibility of 1850 A. U. radiation.

2. An electric discharge lamp as in claim 1 wherein the envelope consists of approximately:

Components: Parts by weight SiOz B203 27 A1203 5 NazO 2 LiOz and CaO Balance 3. An electric discharge lamp for generating 1850 A. U. radiation and adapted to operate on a voltage supply of between approximately and volts, comprising an envelope having a gaseous filling at a pressure between approximately 3.5 and 4.5 mm. and admixed with mercury vapor, a pair of lead in conductors extending interiorly of said envelope, an anchor between said lead in conductors and offset from the ends thereof, a coiled filament section between the interior end of each of said lead in conductors and said anchor, each of said filament sections being coated with emission material about the end of said section adjacent the interior end of said conductors, the total resistance of said filament sections being between approximately 14 and 17.5 ohms and said envelope consisting of a glass which transmits approximately 27% of the l850 A. U. radiation generated.

4. An electric discharge lamp as described in claim 3 wherein said envelope consists of approximately:

Morehead Jan. 8, 1946 

